This application is based on Patent Application Nos. 2000-335185 filed Nov. 1, 2000 and 2001-328302 filed Oct. 25, 2001 in Japan the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method, and specifically, to reduction of an unevenness of density such as what is called black streaks, which may occur at a joint between scanning areas or a neighbor of the joint when printing each of these areas, the printing of each area being completed by scanning a printing head on the each area one or more times.
2. Description of the Related Art
Recently, user""s needs of a high-speed printing operation is increased in printing apparatuses such as ink jet printers, in which ink is ejected to a printing medium for printing. On the other hand, as one of methods for improving print quality, what is called multi-pass printing system is known, which completes printing for a predetermined area by scanning a printing head (this scanning operation in the multi-pass system is hereinafter also referred to as xe2x80x9cpassxe2x80x9d) to the predetermined area a plurality of times to effectively improve the quality. A method of direct achieving the printing, which makes much of high-speed printing operation, in the multi-pass printing system is to reduce a number of passes.
This is easily understood because in a condition that the number of ejection openings in the printing head is fixed, an amount of paper fed at a time decreases with an increase in the number of passes, while the amount of paper fed at a time can be increased by reducing the number of passes. If for example, printing for the area which otherwise can be printed with two passes is executed with one pass, the printing speed can be simply doubled and increased. More specifically, the smaller the number of passes in the multi-pass printing system, the less the number of scanning operations of the printing head required to print a predetermined area (for example, one sheet of printing medium) is, and the more the amount of paper fed at a time is. Then, the time required for printing the predetermined area decreases.
In the case that the printing head provided with a plurality of ejection openings that eject ink (printing liquid) is scanned in a direction perpendicular to an arrangement direction of the ejection openings so as to perform printing, a band-shaped scanning area (hereinafter also referred to as a xe2x80x9cbandxe2x80x9d), width of which is the same as the arrangement width of the ejection openings, as shown in FIG. 24 is defined as an area to which one scanning operation is executed. When printing for this band is performed with one pass, an amount of ink ejected at one scanning operation to a unit area of a printing medium (hereinafter the amount can be expressed by the number of dots formed on the unit area and the amount is referred to as the xe2x80x9cdutyxe2x80x9d) is larger than that in the multipass printing in which printing for one band is performed with two or more times of scanning operations. Owing to this greater amount of ink, the one-pass printing system easily causes what is called a black streak, which is caused as a portion of higher density at a boundary between the bands (herein after simply referred to as xe2x80x9cjointxe2x80x9d) or at vicinity of the joint, especially at a portion of high duty printing data in the scanning area though the conspicuousness of the black streak varies depending on the nature of printing medium or liquids. This is because when the duty is high so that the amount of ink is large, the ink may flow (bleed) from one band to another band to form the high density portion, as described later for FIG. 16.
This black streak also occurs conspicuously in a system having head arrangement called a xe2x80x9clateral arrangementxe2x80x9d in which the printing heads ejecting a plurality of different print inks (cyan, magenta, yellow, and the like) are arranged in their scanning direction. This is because the joints for all the inks occur at the same location. FIG. 9 schematically shows the lateral arrangement of printing heads. In the case that printing is performed by means of all the ejection openings of the respective printing head of this lateral arrangement, the ejection openings in the printing heads of the respective color inks are scanned to the same area. Thus, the position of the joint cannot be differentiated for each color ink either in the one-pass printing or the multipass printing. As a result, an amount of ink ejected to the vicinity of the joint become large as same as to another area in the band. In the example shown in FIG. 9, the amount corresponds to an amount of three color inks, that is, Y, M, and C inks. Accordingly, an amount of ink flown into from the adjacent band becomes large, resulting in more noticeable black streaks.
The black streak, which occurs at the boundary between bands or at the vicinity of the boundary as described above are also called a xe2x80x9cjoint streakxe2x80x9d or a xe2x80x9cbandingxe2x80x9d. In case that the joint streak is conspicuous, the print quality may be such that printed materials obtained cannot be put to practical use.
On the other hand, methods of reducing such joint streak in the one-pass printing to improve the image quality have been proposed.
For example, Japanese Patent Application Laid Open No.11-188898 discloses a method of thinning printing data, in which when completing printing of an image one band by one band by scanning the printing head repeatedly in a main scanning direction, at least one of a first raster or a last raster in printing data for one band is divided into unit areas each consisting of a predetermined number of pixel and printing data for each unit area is thinned in a manner that an ejection amount of object color ink of thinning process and an ejection amount of another color inks are calculated based on printing data of the unit area and based on the sum of calculated amount printing data is thinned so as to decrease the ejection amount of the object color ink.
Further, Japanese Patent Application Laid Open No. 04-33470 proposes a method of identifying a printing medium used for printing and varying a correction amount for printing data on based on the result of the identification.
However, the conventional methods of reducing the joint streak can not provide a sufficiently accurate control of thinning especially in relation to a kind of the printing medium used for printing or the number of passes in the multipass printing system. Consequently, the conventional methods may execute an unwanted thinning process or undergo a reduced printing speed owing to this thinning process.
For example, an increase in the number of passes generally reduces occurring of the joint streak. However, when this increasing the number of passes is simply applied in the case of using ordinary paper, the effect of the thinning process may become so high that a white streak inversely occurs to degrade the printed image. Further, depending on the printing medium used or the number of passes for the multipass printing, there is a case that a correction by means of the thinning process is not required. The correction for the printing data may be executed even if this correction is not required, thereby reducing the printing speed.
The object of the present invention is to provide an ink jet printing apparatus and an ink jet printing method which can print color images with decreased joint streaks regardless of a type of the printing medium or the number of passes and can prevent a printing speed from decreasing when no correction for the joint streak are required.
In the first aspect of the present invention, an ink jet printing apparatus using a printing head and relatively scanning the printing head to a printing medium to perform printing by ejecting a plurality of colors of ink from the printing head, the apparatus comprising:
determining means for determining whether to reduce an amount of ink to be ejected to a vicinity of a joint in a band on the printing medium, the band being defined by the joint and defined as an area printed by scanning the printing head, based on printing method information added to printing data; and
printing control means for when the determining means determine to reduce the amount of ink, correcting the printing data so that the amount of ink ejected to a predetermined area in the vicinity of the joint during the scanning is decreased at a decreasing rate corresponding to an amount of ink to be ejected based on the printing data, and controlling the printing apparatus to perform printing according to a printing method designated by the printing method information, based on the corrected printing data,
and when the determining means determine not to reduce the amount of ink, controlling the printing apparatus to perform printing according to a printing method designated by the printing method information, based on the printing data without executing correcting of the printing data for decreasing an amount of ink ejected during the scanning.
In the second aspect of the present invention, an ink jet printing method using a printing head and relatively scanning the printing head to a printing medium to perform printing by ejecting a plurality of colors of ink from the printing head, the method comprising the steps of:
determining whether to reduce an amount of ink to be ejected to a vicinity of a joint in a band on the printing medium, the band being defined by the joint and defined as an area printed by scanning the printing head, based on printing method information added to printing data; and
when the determining step determine to reduce the amount of ink, correcting the printing data so that the amount of ink ejected to a predetermined area in the vicinity of the joint during the scanning is decreased at a decreasing rate corresponding to an amount of ink to be ejected based on the printing data, and controlling the printing apparatus to perform printing according to a printing method designated by the printing method information, based on the corrected printing data,
and when the determining step determine not to reduce the amount of ink, controlling the printing apparatus to perform printing according to a printing method designated by the printing method information, based on the printing data without executing correcting of the printing data for decreasing an amount of ink ejected during the scanning.
In the third aspect of the present invention, a data processing method used in an ink jet printing apparatus using a printing head and relatively scanning the printing head to a printing medium to perform printing by ejecting a plurality of colors of ink from the printing head, the method comprising the steps of:
determining whether to reduce an amount of ink to be ejected to a vicinity of a joint in a band on the printing medium, the band being defined by the joint and defined as an area printed by scanning the printing head, based on printing method information added to printing data; and
when the determining step determine to reduce the amount of ink, correcting the printing data so that the amount of ink ejected to a predetermined area in the vicinity of the joint during the scanning is decreased at a decreasing rate corresponding to an amount of ink to be ejected based on the printing data, and controlling the printing apparatus to perform printing according to a printing method designated by the printing method information, based on the corrected printing data,
and when the determining step determine not to reduce the amount of ink, controlling the printing apparatus to perform printing according to a printing method designated by the printing method information, based on the printing data without executing correcting of the printing data for decreasing an amount of ink ejected during the scanning.
According to the above configuration, the printing method information, which is added to the printing data, enables the identification of, for example, a type of the print medium and the number of times of scanning operations required to complete printing a band, and then, it can be determined on the basis of the result of the identification whether or not to reduce the amount of ink landing on the vicinity of a joint. When it is determined that the amount of ink landing on the vicinity of the joint is to be reduced, a printing operation is executed according to the printing method indicated by the printing method information, and a process is executed so that the amount of ink ejected during the scanning operation is reduced at a reduction rate corresponding to the amount of ink landing on a predetermined area in the vicinity of the joint on the basis of the printing data. On the other hand, when it is determined that the amount of ink is not to be reduced, the printing operation is executed according to the printing method indicated by the printing method information without reducing the amount of ink ejected during the scanning operation. Consequently, in the case that the amount of ink is to be reduced, a proper ink amount reduction, which agrees with the type of the printing medium and the number of times of scanning operations indicated by the printing method information, can be executed. On the other hand, when it is determined that the amount of ink is not to be reduced, the restraint of the occurrence of the streak can be achieved by performing the printing operation according to the printing method with no process for reducing the amount of ink. Furthermore, an unwanted process for reducing the amount of ink can be avoided.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.